Method of using surface material of molding surface of mold

ABSTRACT

Surface material of a mold molding surface and surface treatment method. A molding surface of material including metal and in which the molding surface reaches 50° C. or higher during molding is subjected to rapid thermal processing by injecting a substantially spherical shot with a hardness equal to or greater than the surface hardness of the mold and a size of #220 (JIS R6001-1973) or smaller at an injection pressure of 0.2 MPa or more and bombarding the surface with the shot, causing the temperature to rise locally and instantaneously at a bombarded portion to refine the surface structure of the surface and to form numerous smooth arc-shaped indentations on the entire surface of the surface. Then, powder including titanium having size of #100 or smaller is injected at an injection pressure of 0.2 MPa or more to form a coating of titanium oxide on the surface of the surface.

FIELD OF THE INVENTION

The present invention relates to a surface material of a molding surfaceof a mold (hereinafter, referred to simply as “molding surface”) and toa method for surface treatment of a molding surface to obtain thesurface material, and more specifically to a surface material of amolding surface of a mold and to a method for surface treatment of themolding surface having the objective of improving wear resistance,corrosion resistance, and demoldability.

BACKGROUND OF THE INVENTION

In order to extend the lifespan of a mold employed for molding a resinor the like, strengthening of the molding surface is performed toimprove the wear resistance of the molding surface of the mold, whichcontacts the material being molded.

In particular, in a mold for molding a resin material, to which a fillermade from a powder, fibers or the like of glass, ceramic, or metal etc.has been added at a high blending proportion of from 40% to 50% in orderto improve the strength of a molded article, the molding surface is evenmore readily worn by contact with such a filler. This accordingly leadsto even higher demands for strengthening in order to impart wearresistance or the like.

Moreover, the molding surface employed for molding resin is susceptibleto corrosion from contact with a corrosive gas given off from resinheated to high temperature, and from corrosive substances and the likeadhering thereto. The smoothness of a surface of the mold is lost whencorrosion occurs, which in turn leads to the generation of defectivemolding accompanying reduced demoldability and the transfer of holes(pitting corrosion) arising due to corrosion, and to defective moldingand the like generated by the incorporation of dirt that had been bakedon to the surface of the mold into the article being molded.

This means that as well as demand for the wear resistance describedabove, there is also demand for high corrosion resistance for a moldingsurface of a mold, and in particular for a molding surface of a mold formolding a molding material such as a synthetic resin or rubber thatgenerates corrosive gas or corrosive adhering substances.

In relation to corrosion resistance out of the above problems, molds aremanufactured using high corrosion resistant stainless steels, however,it is not possible to completely prevent the occurrence of corrosion byusing such high corrosion resistant stainless steels. Moreover, althoughan improvement in the corrosion resistance can be expected by using sucha surface material for the molding surface and by the treatment methodthereof, such an approach does not enable wear resistance to be improvedby hardening at the same time.

In order to improve wear resistance by hardening, in cases in which anattempt is made to increase corrosion resistance at the same time,generally a hard substance is employed for the surface for molding ofthe mold and this is then coated with a coating film configured from ahighly corrosion resistant material. An improvement in both wearresistance and corrosion resistance is achieved by performing variousplating treatments on the surface of the molding surface, such as nickelplating, chromium plating, etc., or by performing ceramic coating ordiamond-like carbon (DLC) coating using PVD or CVD.

Moreover, prior to performing such coating, various types of heattreatment and nitriding treatment are also employed in combination onthe surface of a base material to achieve even greater hardening.

Note that although not entirely preventing corrosion of a mold, asurface treatment by shot peening is known as a method to prevent theoccurrence of stress corrosion cracking which can occur with corrosion.

Namely, one cause of stress corrosion cracking occurring is the presenceof tensile stress, and the generation of stress corrosion cracking issuppressed by performing shot peening on the surface of a mold torelease the tensile stress and to also impart a compressive residualstress thereto.

Moreover, although not prescribed for surface treatment to a mold, inorder to further improve the corrosion resistance of a corrosionresistant metal, the present applicant has already filed and receivedregistration for a Japanese Utility Model Application for the followinghigh corrosion resistant metal. In the registered Japanese UtilityModel, a surface of a substrate of stainless steel or the like issubjected to the ejection of a powder having a hardness of not less thanthat of the substrate at an ejection velocity of not less than 50 m/s,or at an ejection pressure of not less than 0.29 MPa. The metalstructure at the substrate surface is strengthened and hardened byforming a layer from fine crystals having a particle diameter of notmore than 1 μm. The substrate surface formed with the fine crystal layeris then subjected to ejection of an ejection powder arising from mixinga titanium or titanium alloy powder with a precious metal powder at anejection velocity of not less than 80 m/s, or at an ejection pressure ofnot less than 0.29 MPa. A titanium oxide coating film of supporting theprecious metal and/or an oxide of a precious metal is thereby formed onthe surface of the substrate, so as to produce the high corrosionresistant metal (see claim 1 and the like of Patent Document 1).

PRIOR ART DOCUMENTS Patent Documents

-   Patent Document 1: Japanese Utility Model Registration No. 3150048

Problems to be Solved by the Invention

From out of a surface materials of a molding surface of a mold and amethod for surface treatment to obtain such a surface material asdescribed above, a method to coat the surface of a base material ofmetal mold with a coating using various types of plating and PVD or CVDcan be used to raise the surface hardness by covering the surface of thebase material with a hard coating film. Not only can the wear resistancebe improved in this manner, but the corrosion resistance can also beimproved by covering the surface of the base material and stoppingcontact with corrosion-causing oxygen and water, and corrosive gases andthe like.

However, raising the corrosion resistance and the wear resistance bycoating surfaces of molds increases the manufacturing cost of molds dueto increasing the number of manufacturing processes in order to performcoating. In particular for DLC coating, there is a dramatic rise incost, due to the expense thereof.

Moreover, forming a coating film changes the dimensions of a mold, andso a base material needs to be processed to dimensions that consider thecoating film forming. There is also a need to tightly control coatingthickness during film forming, and a need to perform processing and filmforming at high precision.

Moreover, in cases in which wear resistance and corrosion resistance isimparted by forming a coating film, the effectiveness of both the wearresistance and corrosion resistance is lost when the coating film isdamaged (such as by cracks, delamination, etc.).

Moreover, from out of the method for surface treatments described above,although shot peening is effective as a method to prevent stresscorrosion cracking by imparting compressive residual stress to thesurface of the mold, shot peening is not able to prevent corrosionitself, and so is not able to prevent the generation of corrosions suchas grain boundary corrosion.

Note that the method for surface treatment introduced in Patent Document1 attempts to harden the surface of the substrate by forming the finecrystal layer described above, and enables a titanium oxide coating filmhaving a high strength of adhesion to be formed by forming a coatingfilm of titanium oxide supporting a precious metal and/or an oxide of aprecious metal above the fine crystal layer. Oxidation of the substrateis proactively prevented by reducing capabilities exhibited by thistitanium oxide coating film having a photocatalytic action. As a result,not only is a high corrosion resistance obtained, but it is alsopossible to achieve both effects of an improvement in hardening andcorrosion resistance at the same time using the comparatively simplytreatment of ejecting a powder or granules.

However, the improvement in corrosion resistance through the methoddescribed in Patent Document 1 is an improvement in corrosion resistanceachieved by utilizing the reducing capabilities exhibited by aphotocatalytic action as determined by performing tests underirradiation of “sunlight (daytime)” (paragraph [0088] of Patent Document1). Thus a loss of the corrosion resistance effect exhibited by thephotocatalytic action would be expected in cases in which application ismade to a metal article employed in a state in which light is blocked,as is the case for a molding surface of a mold.

An objective of the present invention is accordingly to use acomparatively simple method of ejecting a powder or the like, similar tothat of the invention described in the Patent Document 1 listed above,to provide a surface material for a molding surface of a mold, and amethod for surface treatment to obtain this surface material, with thesurface material and method for surface treatment capable of hardening asurface of a mold and achieving an improvement in corrosion resistance,as well as also improving demoldability.

SUMMARY OF INVENTION Means for Solving the Problem

In order to achieve the objective of the present invention, a surfacematerial of a molding surface of a mold according to the presentinvention comprises:

-   -   a micronized surface structure on at least the molding surface        of the mold made from a metal, or a substance including a metal,        for which the molding surface reaches 50° C. or hotter during        molding;    -   innumerable smooth circular arc shaped depressions lacking        pointed protrusions formed on an entire surface of the molding        surface; and    -   a titanium oxide coating film formed on a surface of the molding        surface.

Preferably, the metal is a metal susceptible to corrosion.

Preferably, the mold is a mold employed for molding a food product, athermoplastic resin, a thermoset resin, a natural rubber, or a syntheticrubber.

Preferably, the mold is a mold employed for molding a resin in which themolding surface reaches from 100° C. to 400° C. during molding throughcontact with molten resin or the like or through heating the molditself.

Furthermore, in order to achieve the objective of the present invention,a method for surface treatment of a molding surface according to thepresent invention comprises:

ejecting substantially spherical shot against at least the moldingsurface of the mold made from a metal or a substance including a metalfor which the molding surface reaches 50° C. or hotter during molding,the substantially spherical shot having a size of 220 grit (JISR6001-1973) or finer and having a hardness equivalent to or harder thana surface hardness of the mold, the substantially spherical shotejection being at an ejection pressure of not less than 0.2 MPa so as toperform instantaneous heat treatment by impact of the substantiallyspherical shot causing a local and instantaneous rise in temperature atimpacted portions, so as to micronize a surface structure of the moldingsurface and form innumerable smooth circular arc shaped depressions overan entire surface of the molding surface; and

-   -   forming a titanium oxide coating film on the molding surface by        ejecting a powder formed from titanium or titanium alloy having        a size of 100 grit (JIS R6001-1973) or finer by ejecting at an        ejection pressure of not less than 0.2 MPa against a surface of        the mold that had been subjected to the instantaneous heat        treatment so as to form a titanium oxide coating film on a        surface of the molding surface.

It is preferable to perform a preliminary treatment process prior toperforming the instantaneous heat treatment, the preliminary treatmentprocess including ejecting a carbide powder having a size of 220 grit(JIS R6001-1973) or finer by ejecting at an ejection pressure of notgreater than 0.2 MPa against at least the molding surface so as to causecarbon element contained in the carbide powder to diffuse into thesurface of the mold.

Preferably, the carbide powder ejected in the preliminary treatmentprocess is a silicon carbide (SiC) powder.

Effect of the Invention

In the present invention as described above, the surface material of amolding surface of a mold and the method for surface treatment to obtainthis surface material enable not only the molding surface, whichhitherto has been processed to a specular (mirror) finish by a methodsuch as hand polishing or the like, to be imparted with improved moldingsurface hardness and wear resistance by treatment with blast processingthat is a comparatively simple method, but also enable an improvement inantifouling effect and corrosion resistance to be achieved.

As a result, in the present invention, the surface material of a moldingsurface of a mold and a mold treated with the method to obtain thissurface material both enable surface treatment of a mold to be performedcomparatively more simply than cases in which, as described above, handpolishing is performed and then after hand polishing a coating film isformed by plating or by PVD or CVD. Molds can accordingly bemanufactured with a shorter lead time and for a cheaper price. Moreover,the lifespan of a mold is extended by improving the wear resistance byhardening and by improving the corrosion resistance, thereby enablingthe manufacturing cost of articles to be molded to be greatly reduceddue to being able to reduce the defect rate when molding.

Note that in the present invention, the surface material of a moldingsurface of a mold and a mold on which surface treatment has beenperformed by the method to obtain this surface material, theadvantageous effects of corrosion resistance and antifouling describedabove are thought to be effects produced by a titanium oxide coatingfilm formed on the molding surface exhibiting a photocatalyst-likefunction. However, this result, i.e. a corrosion resistance andantifouling effect being exhibited by forming a titanium oxide coatingfilm on a molding surface of a mold not irradiated with light duringmolding a molding material, is an unexpected effect.

Thus although the reasons are not fully understood as to why theadvantageous effects of corrosion resistance and antifouling wereobtained on a molding surface of a mold not irradiated with light duringmolding, it is thought that heating or warming of the molding surfaceduring molding resulted in catalytic activation by the heat therefrom.The advantageous effects of improved corrosion resistance andantifouling and the like are thought to arise from a reducing action ofthe oxide, and from the decomposition of corrosive gases and adheringsubstances due to the degradative ability of organic materials, and fromantifouling and the like due to hydrophilic properties being exhibited.

Thus an improvement in corrosion resistance and prevention of dirtadhering is achieved by applying in the present invention the surfacematerial of a molding surface of a mold and a mold treated with thetreatment method to obtain this surface material, to a mold with amolding surface that reaches 50° C. or hotter during molding, and inparticular to a mold employed for molding resins in which thetemperature of the molding surface during molding is, for example, from100° C. to 400° C.

Moreover, in cases in which the surface material of a molding surface ofa mold according to the present invention and the method for surfacetreatment are applied to a mold employed for molding a thermoplasticresin or rubber, in addition to improving the corrosion resistance bythe reducing capabilities, an improvement in corrosion resistance isalso obtained by decomposition of corrosive gases and adheringsubstances arising from the molding material in a heated state. Badsmells are also reduced by such decomposition, and so an improvement inthe work environment can also be achieved.

Furthermore, in cases in which a preliminary treatment process isperformed of ejecting a specific carbide powder, for example a siliconcarbide (SiC) powder, against a molding surface of a mold prior toinstantaneous heat treatment, carbon in the carbide powder diffusing andpenetrating into (carburizing) the surface of the mold enables thehardness in the vicinity of the surface for molding to be raised evenmore, and enables a greater improvement in wear resistance and the liketo be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photograph capturing a surface state after a CASS test forat test strip (untreated).

FIG. 2 is a photograph capturing a surface state after a CASS test forat test strip (Example).

EMBODIMENTS TO CARRY OUT THE INVENTION

A surface material of a molding surface of a mold according to thepresent invention and a method for surface treatment for a moldingsurface of a mold to obtain the surface material are described below.

Treatment Subject: Molding Surface of Mold

The method for surface treatment of the present invention is a method oftreatment having at least a molding surface of a mold as the treatmentsubject, and so the method for surface treatment of the presentinvention may be executed on just the molding surface, or may beexecuted on the entire mold including the molding surface thereof.

There is no particular limitation to the application of the moldsubjected to treatment, and as long as the mold is employed in anapplication in which the molding surface reaches 50° C. or hotter duringmolding, the subjected mold may be a mold employed in variousapplications, such as for molding a food product, for molding athermoplastic resin or a thermoset resin, or for molding a rubber.However, particularly preferable application is made to a mold formolding resins in which the molding surface reaches a temperature in thevicinity of from 100° C. to 400° C. during molding due to contact withmolten resin or the like, or due to heating of the mold itself.

The substance of the mold subjected to treatment is not particularlylimited as long as it contains a metal susceptible to corrosion. Forexample, molds of various steels generally employed for molds, such asstainless steels (SUS materials), carbon tool steels (SK materials), oralloy tool steels (SKS, SKD, SKT materials), may each be subjected tothe treatment of the present invention. Moreover, molds of varioussubstances may be subjected to treatment, such as molds made from othersteel materials such as high speed tool steels (SKH materials), sinteredmetals such as cemented carbides, Cu—Be alloys, and molds made fromother non-ferrous metal alloys.

Moreover, the mold is not necessary formed entirely of a metal material,and may be a mold that includes other components, such as ceramics forexample.

Surface Treatment

The surface treatment of the present invention as described below isperformed on at least a surface of a molding surface of one of the moldsdescribed above.

Preliminary Treatment Process

The present process (preliminary treatment process) is a processperformed as required, and as such is a process that is not necessarilyalways performed depending on the application etc. for the mold, and isnot an essential process of the present invention.

In the present process, a carbide powder is dry-ejected against asurface of a mold so as to prepare the surface by removing an electricaldischarge hardened layer and softened layer arising on the surface ofthe mold due to electrical discharge processing or cutting processingduring mold fabrication, or by removing directional processing marks(cutting marks, polishing marks, tool marks and the like) generatedduring machining, grinding, and polishing processes. In additionthereto, carbon element present within the carbide powder is caused todiffuse and penetrate into the surface of the mold, so as to performcarburizing at normal temperatures.

Examples of carbide powders that may be employed include the powders ofcarbide or carbon containing substances such as B₄C, SiC (SiC(α)), TiC,VC, graphite, diamond, and the like. SiC is preferably employedtherefor, and SiC(α) is more preferably employed therefor.

When employed either for the objective of removing an electricaldischarge hardened layer or softened layer, or removing directionalprocessing marks, so that the carbide powder employed exhibits a highcutting force, preferably an angular powder is employed therefor thathas been obtained for example by crushing a sintered carbide basedceramic and then sieving. The shape of the carbide powder is notparticularly limited in cases lacking such a cutting objective, and acarbide powder with a spherical shape or one with various other shapesmay be employed.

In order to obtain an ejection velocity required to achieve diffusionand penetration of carbon element, the size of the powder employed has asize of 220 grit (JIS R6001-1973) (from 44 μm to 105 μm) or finer, andpreferably the powder employed has a size of so-called “fine particles”of 240 grit (JIS R6001-1973) (average of average diameter from 73.5 μmto 87.5 μm) or finer.

Various known blasting apparatuses capable of dry-ejecting a powder maybe employed as the method for ejecting such a carbide powder onto anarticle to be treated. An air blasting apparatus is preferably employedtherefor due to the comparative ease with which the ejection velocityand the ejection pressure can be adjusted.

A direct pressure blasting apparatus, suction gravity blastingapparatus, or various other types of blasting apparatus may be employedas such an air blasting apparatus. Any of these types of blastingapparatus may be employed, and the type thereof is not particularlylimited as long as it has the performance capable of dry-ejecting at anejection pressure of 0.2 MPa or above.

When a carbide powder as described above is dry-ejected at high speedusing such a blasting apparatus against a surface of a mold at portionsof the surface of the mold that will contact with the molding material,electrical discharge hardened layers and softened layers, directionalprocessing marks, and the like arising during mold fabrication fromelectrical discharge processing and cutting processing are removed so asto prepare a non-directional mold surface.

Moreover, the impact of the carbide powder against the surface of themold causes localized temperature rises on the surface of the mold atportions impacted by the carbide powder. The carbide powder is alsoheated and undergoes thermal decomposition. As the carbon elementpresent within the carbide of the carbide powder diffuses and penetratesinto the surface of the mold, the carbon content of these portionsincreases, enabling the hardness of the surface of the mold afterperforming the preliminary treatment process to be greatly increased.

In the preliminary treatment of the present invention, the carbidepowder undergoes decomposition through thermal decomposition due to thetemperature of the carbide powder rising when the carbide powder iscaused to impact an article to be treated by the blast processing. Thecarburizing treatment is accordingly performed by thus generated carbonelement present within the carbide powder accordingly diffusing andpenetrating into the article to be treated.

According to the preliminary treatment of this method, the diffusion andpenetration of carbon element into the mold is most significant at thegreatest proximity to the surface, with this also resulting in a greatincrease the carbon content. The carbon content increases due todiffusion toward the inside of the article to be treated. This resultsin the generation of a tilting structure in which the carbon contentgradually decreases with depth from the surface of the article to betreated, with the carbon content decreased to that of an untreated stateby a certain depth.

The carbide powder and the article to be treated undergo a partial risein temperature when the carbide powder impacts the article to betreated. However, the rise in temperature is only localized andinstantaneous. Distortion, phase transformation, or the like in thearticle to be treated, such as that caused by heat treatment in anordinary carburizing treatment performed by heating the entire mold in acarburizing furnace, is accordingly not liable to occur. Moreover,higher adhesion strength is achieved due to the generation of finecarbides, and an irregular carburized layer is not generated.

Instantaneous Heat Treatment Process

The present process (instantaneous heat treatment process) is performedon at least a molding surface of a mold subject to treatment (a moldingsurface of a mold after the preliminary treatment process in cases inwhich the preliminary treatment process described above has beenperformed). The present process is performed to achieve a surfaceprofile that improves the demoldability by dry-ejecting a sphericalpowder against the surface of the mold so as to form innumerable finedepressions having a circular arc shape on the surface of the mold, andso as to further increase the surface hardness by micronization ofstructure in the vicinity of the surface of the molding surface.

There are no particular limitations to the substance of the sphericalpowder employed therefor, as long as the spherical powder has a hardnessequal to or more than the hardness of the mold to be treated. Forexample, as well as spherical powders made from various metals, aspherical powder made from a ceramic may be employed, and a sphericalpowder made from a similar substance to the powders of carbon or carboncontaining substances described above may also be employed therefor.

The spherical powder employed is spherical to an extent that enablesinnumerable fine indentations having a circular arc shape as describedabove to be formed on the surface of the mold.

Note that “spherical shaped” in the present invention need not referstrictly to a “sphere”, and also encompasses non-angular shapes close tothat of a sphere.

Such spherical powders can be obtained by atomizing methods when thesubstance of the powder is a metal, and can be obtained by crushing andthen melting when the substance of the powder is a ceramic. In order toachieve the ejection velocity needed to plastically deform the surfaceof the mold by impact to form semi-circular indentations (dimples), theparticle diameter of the powder employed therefor has a size of 220 grit(JIS R6001-1987) (from 44 μm to 105 μm) or finer, and preferably “fineparticles” having a size of 240 grit (JIS R6001-1973) (average ofaverage diameter from 73.5 μm to 87.5 μm) or finer are employedtherefor.

Moreover, various known blasting apparatuses with dry-ejectioncapabilities, similar to those explained with respect to the ejectionmethod for carbide powder when explaining the preliminary treatmentprocess, may be employed as the method for ejecting the spherical powderonto the surface of the mold in such a manner. The type and the like ofthe blasting apparatus is not particularly limited, as long as it hasthe performance capable of ejecting at an ejection pressure of at least0.2 MPa.

The spherical powder such as described above is ejected against thesurface for molding of the mold, and the impact of the spherical powderresults in plastic deformation occurring on the surface the mold at theportion impacted by the spherical powder.

As a result, even in cases in which the preliminary treatment processhas been performed by employing the angular carbide powder, and even incases in which indentations and protrusions having acute apexes wereformed on the surface of the mold in the cutting achieved by the impactof such a carbide powder, the surface roughness is improved bycollapsing the acute apexes, and by randomly forming innumerable smoothdepressions (dimples) with circular arc shapes on the entire surface ofthe mold.

Moreover, due to forming the dimples, a surface with improveddemoldability is formed due to the incorporation of air and releaseagent into the dimples during molding reducing the contact area betweenthe molding material and the molding surface.

Moreover, due to the heat generated when impacted by the sphericalpowder, the impacted portions experience instantaneous local heating andcooling. Accompanying the instantaneous heat treatment, fine crystalsare also formed at the surface of the mold and the surface of the moldundergoes work hardening due to plastic deformation when the circulararc shape depressions are formed. The surface hardness of the mold isthereby further increased from that of the state after the preliminarytreatment process. Moreover, due to a compressive residual stress beingimparted by the plastic deformation of the surface, this is also thoughtat the same time to contribute to an increase in the fatigue strengthand the like of the mold, in an effect obtained by so-called “shotpeening”.

Titanium Powder Ejection

A powder of titanium or titanium alloy (hereafter also referred tocollectively as a “titanium powder”) is also ejected against at leastthe molding surface after being subjected to the instantaneous heattreatment as described above. A titanium oxide coating film is therebyformed on the surface for molding of the mold.

Such a titanium powder is not particularly limited in shape as long asthe titanium powder has a size of 100 grit (JIS R6001-1973) (from 74 μmto 210 μm) or finer, and the titanium powder employed may be spherical,angular, or various other shapes.

Moreover, a powder of a precious metal (such as Au, Ag, Pt, Pd, or Ru)having an effect of promoting the catalytic function of the titaniumoxide may be mixed in with the titanium powder at a range of from about0.1% to about 10% mass ratio, and ejected therewith.

Note that in the following description, the term titanium powder isemployed as a collective term that encompasses titanium powdersincorporating a precious metal, unless explanation particularlydifferentiates between a precious metal powder and a titanium powder.

In cases in which a titanium powder mixed with a precious metal powderis ejected, the particle diameters of both powders are not necessarilyalways the same diameter, and a titanium powder and a precious metalpowder having different particle diameters may be employed.

In particular, the specific weight of precious metal powders is greaterthan that of titanium powders, and the particle diameter of the preciousmetal powder may be made smaller than that of the titanium powder so asto bring the masses of each particle of the two powders closer together,and to adjust such that the ejection velocities of both powders aresubstantially the same as each other.

Moreover, various known blasting apparatuses with dry-ejectioncapabilities, similar to those explained with respect to the ejectionmethod for carbide powder or spherical shot when explaining thepreliminary treatment process or the instantaneous heat treatmentprocess, may be employed as the method for ejecting the titanium powderdescribed above onto the surface of the mold. The type and the like ofthe blasting apparatus is not particularly limited, as long as it hasthe performance capable of ejecting at an ejection pressure of at least0.2 MPa.

Ejecting the titanium powder as described above to cause the titaniumpowder to impact against the molding surface including the surfacefinely crystalized by the instantaneous heat treatment process resultsin the velocity of the titanium powder changing between before and afterimpact, and in energy of an amount equivalent to the deceleration invelocity becoming thermal energy that locally heats the impactedportions.

The titanium powder configuring the ejection powder is heated at thesurface of the substrate by this thermal energy, and the titanium isactivated and adsorbed to the substrate surface and diffuses andpenetrates therein. When this occurs, the surface of the titanium reactswith oxygen present in compressed gas or oxygen present in theatmosphere, and is oxidized thereby so as to form a titanium oxide(TiO₂) coating film corresponding to the blend amounts in the ejectionpowder.

The film thickness of the titanium oxide coating film is about 0.5 μm,and is activated and adsorbed to the micronized surface structure formedon the molding surface by the instantaneous heat treatment. The titanium(titanium and precious metal in cases containing a precious metalpowder) diffuses and penetrates inward from the substrate surface to adepth of about 5 μm.

Note that the titanium oxide coating film formed in this manner isoxidized by reaction with oxygen in compressed gas or the atmosphere dueto heat generated during impact. This means that a tilting structure isgenerated in which there is a lot of bonding with oxygen in the vicinityof the surface where the temperature is highest, and the amount ofbonding with oxygen gradually decreases on progression further inwardfrom the surface.

EXAMPLES

The following Test Examples 1 to 4 illustrate examples in which themethod for surface treatment of the present invention is applied tovarious molds, and the Test Example 5 illustrates a result when anevaluation test for corrosion resistance is performed on a test stripthat has had the surface treatment of the present invention performedthereon.

Test Example 1: Pudding Mold

(1) Treatment Conditions

A mold (Example 1) was produced by performing instantaneous heattreatment and titanium powder ejection under the conditions listed inTable 1 below to all faces, including a molding surface of a mold madefrom stainless steel (SUS 304) employed for molding puddings (a foodproduct). The instantaneous heat treatment alone was performed toproduce another mold (Comparative Example 1).

TABLE 1 Pudding Mold (SUS 304) Treatment Conditions Puding Mold SUS 304(380 HV) (φ50 mm x height 30 mm x thickness 1 mm) Product to be MoldedPudding (food product) Instantaneous Heat Treatment Titanium PowderEjection Blasting Apparatus Gravity Type (SGF-4A: made by ZujiManufacturing Co. Ltd) Ejection Substance alumina-silica beads puretitanium Material (hard beads FHB) (TIROP-150: made by Sumitomo SitixCorporation) Grain Size 400 grit 100 grit or finer (from 38 μm to 53 μmdiameter) (from 45 μm to 150 μm diameter) Ejection Pressure 0.4 MPa 0.5MPa Nozzle Diameter φ 9 mm long φ 9 mm long Ejection Distance 200 mm 150mm Ejection Time All faces: 30 seconds × All faces: 30 seconds × 6directions 6 directions

(2) Test Method and Test Results

Puddings were consecutively manufactured while respectively employingthe mold of Example 1 (instantaneous heat treatment+titanium powderejection) and the mold of Comparative Example 1 (instantaneous heattreatment alone).

A so-called “baked pudding” was manufactured as the pudding by putting amold containing a pudding liquid into an oven and heating.

After the pudding liquid filling the mold had been caused to solidify inthe mold by the heat from the oven so as to mold the pudding, asubsequent operation was performed to remove the finished pudding fromthe mold. The “lifespan” was evaluated as the point when the mold wasreplaced accompanying a deterioration in demoldability, and dirt on themolding surface and demoldability were evaluated. The results thereofare listed in Table 2.

Note that the temperature (maximum value) at the molding surface duringpudding manufacture (during molding) rises to 180° C., this being thetemperature of the oven.

TABLE 2 Pudding Mold Test Results Surface Roughness LifespanDirt/Demoldability (Ra) Comparative 0.3 μm 10,000 hours Became graduallymore dirty and Example 1 demoldability gradually deteriorated Example 10.2 μm 20,000 hours Dirt did not adhere and demoldability was also good

(3) Interpretation Etc.

An untreated pudding mold (polished by buffing after press molding) hadpoor demoldability and needed to be replaced at 5,000 hours use. Incomparison to the untreated mold, it was confirmed that not only themold of Example 1, but also of Comparative Example 1, achieved a greatlyextended lifespan, not being susceptible to dirt adhering and exhibitinggood demoldability.

Moreover, whereas the untreated mold had a hardness of 380 HV and aresidual stress of −190 MPa, the mold of the Comparative Example 1subjected to instantaneous heat treatment as described above exhibitedan improvement in surface hardness to 580 HV and an improvement inresidual stress to −1080 MPa. A great reduction achieved in pittingcorrosion generation was confirmed by a test according to the method offerric chloride corrosion tests for stainless steels (JIS G0578:2000).

However, in the mold of Comparative Example 1 subjected to instantaneousheat treatment alone, there was noticeable adherence of dirt thereto anddemoldability deteriorated after 10,000 hours of use, such thatreplacement was required.

In contrast thereto, with the mold of Example 1 subjected to both theinstantaneous heat treatment and titanium powder ejection, neither theadherence of dirt nor a reduction in demoldability was seen even afterexceeding 10,000 hours of use, enabling the lifespan to be extended to20,000 hours of use.

The above results mean that one could say that the above advantageouseffects are obtained in the mold of Example 1 by forming the titaniumoxide coating film on the surface by titanium powder ejection. Thetitanium oxide coating film in the present invention at the surfacematerial for a molding surface of a mold and formed by the treatmentmethod thereof, is accordingly thought to be the entity that decomposeddirt in a state filled with the pudding liquid, and therefor decomposeddirt even in a state in which no light was being irradiated thereon. Thetitanium oxide coating film is also thought to be the entity thatexhibited a photocatalyst-like function of preventing dirt from adheringdue to hydrophilic properties being exhibited.

Although the reason that titanium oxide exhibited a photocatalyst-likefunction even in an environment not irradiated with light in this manneris not completely clear, industrially manufactured titanium oxide losesoxygen when heated to a high temperature, and changes from a white colorto a black color. The material that has turned such a black colorexhibits the properties of a semiconductor. Namely, semiconductor-likeproperties are exhibited when in a state in which there is a deficit ofoxygen bonding.

The titanium oxide coating film formed on the surface of a mold in thepresent invention, as stated above, has a tilting structure in which theamount of bonding to oxygen is greatest in the vicinity of the surfaceof the mold, and the amount of bonding to oxygen gradually decreases onprogression inward from the surface. The titanium oxide present insideaccordingly has a deficit of bonding to oxygen, and this is thought tobe the reason why semiconductor-like properties are exhibited thereby.

Thus by being employed under heating, charge migration is thought tooccur due to thermal excitation, so as to have a catalyst-like (referredto as a “semiconductor catalyst-like” in the specification of thepresent invention) function triggering a charge-migration type ofoxidation-reduction effect.

Generally a semiconductor catalyst needs to be a catalyst having aspecial structure, such as being doped with an electron donor element orwith an electron acceptor element. Obtaining the advantageous effect ofexhibiting a catalytic action with heat by using the titanium oxidecoating film obtained by the comparatively simple method of titaniumpowder ejection is an advantageous effect that greatly exceedsexpectations. Note that a catalyst-like action is exhibited even in anenvironment not irradiated with light as described above in a puddingmold with the surface material for a molding surface of a mold ortreated with the treatment method thereof in the present invention, anda catalyst-like function is also exhibited when employed under heatingat 50° C., as illustrated by “Test Example 5” described below. Similaradvantageous effects, such as preventing dirt from adhering, improvingdemoldability, and extending lifespan, are accordingly thought to beobtained even in cases in which, instead of manufacturing a bakedpudding as described above, a mold that has a surface treated with themethod of the present invention is employed to manufacture gelatinpuddings by taking a pudding liquid with added gelatin at about 50° C.to 60° C. and cooling and solidifying the pudding liquid inside themold.

Test Example 2

TPU Molding Mold

(1) Treatment Conditions

A molding surface of a mold made from prehardened steel for use inmolding a thermoplastic polyurethane elastomer (TPU) is subjected topreliminary treatment, instantaneous heat treatment, and titanium powderejection under conditions as listed in Table 3 below to produce a mold(Example 2). A mold (Comparative Example 2) was also produced byperforming only the preliminary treatment and the instantaneous heattreatment thereon.

TABLE 3 Treatment Conditions for Thermoplastic Polyurethane ElastomerMolding Mold Mold Prehardened Steel (NAK 55 made by Daido Steel Co. Ltd:400 HV) Product to be Molded (500 mm × 500 mm × 20 mm) ThermoplasticPolyurethane Elastomer Preliminary Treatment Instantaneous Heat TitaniumPowder Treatment Ejection Blasting Apparatus gravity type (SGF-4A: madeby Fuji Manufacturing Co. Ltd) Ejection Substance SiC HSS pure titaniumMaterial (TIROP-150 made by Sumitomo Sitix Corporation) Grain 220 grit300 grit 100 grit or finer Size (from 44 μm to 105 μm (from 37 μm to 74(from 45 μm to 150 diameter) μm diameter) μm diameter) Ejection Pressure0.3 MPa 0.4 MPa 0.5 MPa Nozzle Diameter φ 9 mm φ 9 mm long φ 9 mm longEjection Distance 100 mm to 150 mm 100 mm to 150 mm 100 mm to 150 mmEjection Time About 5 minutes About 5 minutes About 10 minutes(2) Test Method and Test Results

The mold of Example 2 (preliminary treatment+instantaneous heattreatment+titanium powder ejection) and the mold of Comparative Example2 (preliminary treatment and instantaneous heat treatment alone) wereeach employed for molding a thermoplastic polyurethane elastomer.

When molding, successive operations were performed of filling a moldthat had been heated to 50° C. with a thermoplastic polyurethaneelastomer that had been heated to 220° C., molding, and taking the resinout from the mold after molding. The time when the mold was replaced dueto an accompanying deterioration in demoldability was evaluated as the“lifespan” thereof, and dirt on the molding surface and demoldabilitywere also evaluated. The results thereof are listed in Table 4.

TABLE 4 Resin Mold Test Results Surface Roughness (Ra) LifespanDirt/Demoldability Comparative 0.3 μm 400,000 shots Little dirt adheringExample 2 Slight problems of demolding Example 2 0.3 μm 700,000 shots Nodirt adhering No problems of demolding(3) Interpretation Etc.

In the mold of Comparative Example 2 subjected to the preliminarytreatment and the instantaneous heat treatment, there was little dirtadhering and slight defective molding. However, in the mold of Example 2that had been further subjected to the titanium powder ejection inaddition to the preliminary treatment and the instantaneous heattreatment, there was no dirt adhering nor problems demolding at all.

As a result, the lifespan of the mold of Example 2 was dramaticallyincreased compared to the mold of Comparative Example 2.

The above results mean that one could say that the above advantageouseffects are obtained in the mold of Example 2 by the titanium oxidecoating film formed on the surface by titanium powder ejection. It isthought that the titanium oxide coating film in the present invention ofthe surface material for a mold and formed by the treatment methodthereof was accordingly the entity that decomposed dirt on the moldingsurface employed a state in which no light was being irradiated thereon,and the entity that exhibited a photocatalyst-like function orsemiconductor catalyst-like function of preventing dirt from adheringdue to hydrophilic properties being exhibited.

Test Example 3: Glass Fiber Reinforced PPS Molding Mold

(1) Treatment Conditions

A molding surface of a mold manufactured from prehardened steel for usein molding polyphenylene sulfide (PPS) containing glass fibers at a 40%mass ratio was subjected to preliminary treatment, instantaneous heattreatment, and titanium powder ejection under conditions as listed inTable 5 below to produce a mold (Example 3). A mold (Comparative Example3) was also produced by performing the preliminary treatment and theinstantaneous heat treatment alone.

TABLE 5 Treatment Conditions for Glass Fiber Reinforced PPS Molding MoldMold Prehardened Steel Product to be Molded (STAVAX made by BohlerUddeholm Co., Ltd: 560 HV) (250 mm × 250 mm × 50 mm) PPS (containing 40%glass fiber) Preliminary Instantaneous Heat Titanium Powder TreatmentTreatment Ejection Blasting Apparatus Fine powder type (SGF-4A: made byFuji Direct pressure type Manufacturing Co. Ltd) (FD-4: made by FujiManufacturing Co. Ltd) Ejection Substance SiC HSS pure titanium Material(TIROP-150 made by Sumitomo Sitix Corporation) Grain 400 grit 400 grit100 grit or finer Size (average of average (diameter from 30 (from 45 μmto 150 diameter of from 37 μm to 53 μm μm diameter) μm to 44 μm)diameter) Ejection Pressure 0.3 MPa 0.5 MPa 0.4 MPa Nozzle Diameter φ 9mm φ 9 mm long φ 5 mm long Ejection Distance 100 mm to 150 mm 100 mm to150 mm 150 mm to 200 mm Ejection Time About 4 minutes About 4 minutesAbout 6 minutes(2) Test Method and Test Results

The mold of Example 3 (preliminary treatment+instantaneous heattreatment+titanium powder ejection) and the mold of Comparative Example3 (preliminary treatment and instantaneous heat treatment alone) wereeach employed for molding PPS containing glass fibers at 40% mass ratio.

When molding, successive operations were performed of filling a moldthat had been heated to 150° C. with PPS heated to 300° C., molding, andtaking the resin out from the mold after molding. The time when the moldwas replaced due to an accompanying deterioration in demoldability wasevaluated as the “lifespan” thereof, and dirt on the molding surface anddemoldability were also evaluated. The results thereof are listed inTable 6.

TABLE 6 Test Results for PPS Molding Mold Surface Roughness (Ra)Lifespan Dirt/Demoldability Comparative 0.3 μm 1,500,000 shots Corrosionoccurred Example 3 and dirt adhered Example 3 0.2 μm 3,000,000 shots Nocorrosion occurred Good demoldability(3) Interpretation Etc.

In the mold employed for molding PPS resin reinforced with glass fiber,the molding surface is readily scratched through the high-hardness glassfibers contacting the molding surface. The molding surface is alsoreadily corroded due to the PPS also generating a corrosive gas (acidicgas) containing sulfur and chlorine when the polymer of the PPS itself,or an oligomer component thereof, decomposes at high temperature.

In the mold of Comparative Example 3 subjected to the preliminarytreatment and the instantaneous heat treatment, a dramatic reduction inthe generation of corrosion also be achieved compared to an untreatedmold, and a dramatic reduction in the adherence of dirt could also beachieved therein. However, in the mold of Example 3 further subjected tothe titanium powder ejection in addition to the preliminary treatmentand the instantaneous heat treatment, corrosion no longer occurred andthe mold showed good demoldability, resulting in no dirt adhering norany demolding problems. The lifespan of the mold of Example 3 wasaccordingly improved by a factor of two compared to the mold ofComparative Example 3.

The above results mean that one could say that the above advantageouseffects can be obtained in the mold of Example 3 by forming the titaniumoxide coating film on the surface by the titanium powder ejection. Thesurface material of a molding surface of a mold of the present inventionand the titanium oxide coating film formed by the treatment methodthereof is thought to exhibit a photocatalyst-like function ofpreventing the generation of corrosion on the molding surface notirradiated with light, decomposing dirt, and preventing dirt fromadhering due to hydrophilic properties being exhibited.

Test Example 4: Mold for Rubber

(1) Treatment Conditions

A mold (Example 4) was produced by subjecting a molding surface of aprehardened steel mold employed for molding rubber to preliminarytreatment, instantaneous heat treatment, and titanium powder ejectionunder conditions as listed in Table 7 below, and a mold (ComparativeExample 4) was also produced by performing the preliminary treatment andthe instantaneous heat treatment alone.

TABLE 7 Rubber Mold Treatment Conditions Mold Prehardened Steel (NAK 55made by Daido Steel Co. Ltd: 400 HV) Product to be Molded (450 mm × 450mm × 20 mm) Rubber Preliminary Instantaneous Heat Titanium PowderTreatment Treatment Ejection Blasting Apparatus Gravity type (SGF-4A:made by Fuji Direct Pressure type Manufacturing Co. Ltd) (FD-4: made byFuji Manufacturing Co. Ltd) Ejection Substance SiC HSS pure titanium(TIROP-150 made by Sumitomo Sitix Corporation) Material Grain 220 grit300 grit 100 grit or finer Size (from 44 μm to 105 (from 37 μm to 74(from 45 μm to 150 μm μm diameter) μm diameter) diameter) EjectionPressure 0.3 MPa 0.5 MPa 0.4 MPa Nozzle Diameter φ 9 mm φ 9 mm long φ 5mm long Ejection Distance 100 mm to 150 mm 100 mm to 150 mm 150 mm to200 mm Ejection Time About 5 minutes About 5 minutes About 8 minutes(2) Test Method and Test Results

The mold of Example 4 (preliminary treatment+instantaneous heattreatment+titanium powder ejection) and the mold of Comparative Example4 (preliminary treatment and instantaneous heat treatment alone) wereeach employed for molding a rubber.

When molding the rubber, repeated operations were performed of filling amold that had been heated to 150° C. with a vulcanized rubber, thenclosing the mold and pressing the rubber to harden (direct compressionmolding) and taking the molded article out from the mold afterhardening. The time when the mold was replaced due to an accompanyingdeterioration in demoldability was evaluated as the “lifespan” thereof,and dirt on the molding surface and demoldability were also evaluated.The results thereof are listed in Table 8.

TABLE 8 Mold for Rubber Test Results Surface Roughness (Ra) LifespanDirt/Demoldability Comparative 0.4 μm   750,000 shots Some dirt adheringExample 4 Example 4 0.3 μm 1,000,000 shots No dirt adhering No problemsdemolding

In the mold of Comparative Example 4 subjected to the preliminarytreatment and the instantaneous heat treatment alone there was also agreat reduction in dirt adhering and demolding problems compared to anuntreated mold. However, a further reduction dirt adhering could beachieved in the mold of Example 4 that had been further subjected to thetitanium powder ejection in addition to the preliminary treatment andthe instantaneous heat treatment.

In a mold for rubber, great effort and expense is incurred in operationsto clean the mold after usage. However, in the mold of the presentinvention, a significant reduction could be achieved in the effortincurred for cleaning operations after use, dirt did not adhere evenafter being used for 1,000,000 shots, and the lifespan of the mold couldbe greatly extended.

The above results mean that, due to the mold of Example 4 exhibitingexcellent antifouling properties compared to the mold of ComparativeExample 4, one could say that the above advantageous effects wereobtained in the mold of Example 4 due to forming the titanium oxidecoating film on the surface by the titanium powder ejection. Thetitanium oxide coating film formed in the present invention on thesurface material for a molding surface of a mold is thought to exhibit aphotocatalyst-like or semiconductor catalyst-like function, which is todecompose dirt even on the molding surface for rubber employed in astate not irradiated with light and to prevent dirt from adhering due tohydrophilic properties being exhibited.

Test Example 5: Corrosion Resistance Test

(1) Test Objective

The test objective was to confirm that a mold according to the presentinvention, and a steel surface that had been subjected to the surfacetreatment with the treatment method thereof, would exhibit a corrosioninhibiting effect in an environment not irradiated with light.

(2) Test Method

SUS 304 was welded (TIG welded) and imparted with a tensile residualstress to produce a test strip susceptible to stress corrosion cracking.A CASS test according to JIS H 8502:1999 “7.3 CASS Test Method” was thenperformed on a welded test strip that was otherwise untreated, and on awelded test strip of the mold and molding method for surface treatmentaccording to the present invention (instantaneous heattreatment+titanium powder ejection).

The CASS test performed here differs from a salt spray test performed bysimply spraying salt water, and is a corrosion resistance test performedby spraying a brine adjusted to an acidity of from pH 3.0 to pH 3.2 bythe addition of copper II chloride and acetic acid. This means that theCASS test is a test of corrosion resistance performed in an extremelyhash corrosion environment.

Note that the test conditions of the CASS test are as listed in thefollowing Table 9.

TABLE 9 CASS Test Conditions Item When Adjusted During Test Sodiumchloride concentration in g/L 50 ± 5  50 ± 5 Copper II chloride(CuCl₂•H₂O) 0.26 ± 0.02 concentration in g/L pH 3.0 3.0 to 3.2 Sprayrate in ml/ 80 cm²/h —  1.5 ± 0.5 Temperature inside test chamber — 50 ±2 in ° C. Temperature of brine tank in ° C. — 50 ± 2 Temperature ofsaturated air vessel — 63 ± 2 in ° C. Compressed air pressure in kPa —from 70 to 167(3) Test Result and Interpretation

The state of test strips after the CASS test are illustrated in FIG. 1(untreated) and FIG. 2 (Example).

As illustrated in FIG. 1 , the generation of rust was observed on thesurface of the untreated test strip.

In contrast thereto, on the test strip that had been subjected tosurface treatment for a mold according to the present invention andmethod thereof, no rust generation was observed and the clean statepresent prior to the CASS test was maintained, as illustrated in FIG. 2, confirming that the test strip of the mold according to the presentinvention enabled extremely high corrosion resistance to be obtained.

In shot peening, tensile residual stress that has been generated in atest strip by welding is released, and a compressive residual stress isimparted thereto. This is accordingly known to have an advantageouseffect of inhibiting stress corrosion cracking, however is not known todirectly inhibit corrosion (rust) from occurring.

In the test strip of the surface material of the molding surface of thepresent invention, against rust generation the titanium oxide coatingfilm formed on the surface thereof by titanium powder ejection isaccordingly thought to be the reason a photocatalyst-like or asemiconductor catalyst-like function (reduction function) is exhibited.

Note that a CASS test is a test performed using a lidded test chamber inorder to maintain the environment inside the test chamber in a constantstate, and light is accordingly not irradiated onto the test stripduring testing.

However, the CASS test is performed by testing in a state in which thetemperature inside the test chamber is 50° C.±2° C., and so thetemperature of the test strip is also warmed to 50° C.±2° C. Thetitanium oxide coating film is thought to exhibit the photocatalyst-likeor semiconductor catalyst-like function due to testing being performedin such a warmed state.

Note that the surface roughness Ra was 0.3 μm at a smooth portion in thevicinity of the weld on the test strip of the Comparative Example thathad been subjected to instantaneous heat treatment by the ejection of400 grit (diameter from 30 μm to 53 μm) shot made from HSS ejected at anejection pressure of 0.5 MPa thereon, and the surface hardness wasimproved to 580 HV from an untreated state of 300 HV.

The surface roughness Ra was improved to 0.2 μm at a smooth portion inthe vicinity of the weld on the test strip of the present inventionExample that was a test strip subjected to instantaneous heat treatmentunder the above conditions, and then further subjected to ejection oftitanium powder of particle diameter from 45 μm to 150 μm ejected at anejection pressure of 0.4 MPa. The surface hardness after treatment wasalso maintained without change at 580 HV.

The hardness of titanium is about 300 HV, however the hardness oftitanium oxide (TiO₂), an oxide of titanium, reaches a hardness of 1000HV. Thus the surface hardness of the titanium powder used for ejectionis accordingly a hardness of about 1000 HV and higher than the 580 HVsurface hardness of the test strip after the instantaneous heattreatment from forming an oxide coating film.

Thus in the method for surface treatment of the present invention, thetitanium powder ejection against the surface after instantaneous heattreatment is thought to smooth by pressing and collapsing protrusiontips of surface indentations and protrusions formed by the impact ofshot during the instantaneous heat treatment, so that burnishing isperformed.

Namely, not only are there depressions (dimples) formed by the impact ofshot on the surface of the test strip after instantaneous heattreatment, but a state is achieved in which acute protrusions are alsoformed between one and another of the formed depressions.

In contrast thereto, by further performing the titanium powder ejectionagainst the surface after instantaneous heat treatment, smoothing(burnishing) is achieved by pressing and collapsing the protrusions ofthe indentations and protrusions that had been formed on the surface.The surface achieved thereby, which lacks pointed protrusions and hasbeen deformed into a smoothed profile with depressions alone, is thoughtto be why the numerical value of the surface roughness Ra is reduced.

Thus with the surface material of the molding surface according to thepresent invention, apex portions of pointed protrusions, which wouldresist removal when removing the molded article from the mold, arepressed and collapsed so as to smooth the surface material while leavingthe depressions (dimples) that were generated by the instantaneous heattreatment, into which a release agent and air etc. can be introduced toreduce the contact area between the surface of the molded article andthe surface of the mold. The surface material accordingly not onlyexhibits improved demoldability that accompanies the antifouling andanticorrosion due to the photocatalyst-like or semiconductorcatalyst-like effect of the titanium oxide, but after processing thesurface itself has an improved and superior structure with improveddemoldability.

Summary of Test Results

The Test Examples 1 to 5 as described above had the titanium oxidecoating film formed on the molding surface of the present invention (thesurface of the test strip in the Test Example 5). In each case theresults obtained indicated that, irrespective of the tests beingperformed in state in which light is not irradiated thereon, thetitanium oxide coating film formed on the surface exhibited aphotocatalyst-like function.

However, in each of the Test Examples 1 to 5 described above, the testswere performed in a state in which the molding surface (the surface ofthe test strip in Test Example 5) had been heated or warmed to atemperature of 50° C.±2° C. or hotter. Due to there being no otherenergy present to excite a photocatalyst function of the titanium oxidecoating film, the logical postulation is that the advantageous effectsdescribed above of improved corrosion resistance and antifouling etc.were induced by the heat imparted to the portions formed with thetitanium oxide coating film.

Thus in Test Examples 1 to 5, realization of a photocatalyst-like orsemiconductor catalyst-like function was confirmed (see Test Example 5)in a state in which a sample has been warmed to at least 50° C. (±2°C.). Thus application of the surface treatment of the present inventionto at least a molding surface of a mold having a molding surface thatreaches 50° C. or hotter during molding, enables the followingadvantageous effects to be obtained at the same time: improved wearresistance accompanying raising the hardness of the molding surface;improved corrosion resistance; and improved demoldability.

The invention claimed is:
 1. A method of using a surface material of amolding surface of a mold, the surface material comprising: a micronizedsurface structure on at least the molding surface of the mold made froma metal, or a substance including a metal; circular arc shapeddepressions lacking pointed protrusions formed on an entire surface ofthe molding surface; and a titanium oxide coating film formed on asurface of the molding surface having the micronized surface structure,and having a tilting structure in which an amount of bonding to oxygenis greatest in a vicinity of the surface of the molding surface, andwhen using the surface material, the molding surface on which thetitanium oxide coating film is formed being heated or warmed to 50° C.to 400° C., and no light being irradiated to the molding surface onwhich the titanium oxide coating film is formed.
 2. The method of usingthe surface material of the molding surface of claim 1 wherein the metalis a metal susceptible to corrosion.
 3. The method of using the surfacematerial of the molding surface of claim 1 wherein the mold is a moldemployed for molding a food product, a thermoplastic resin, a thermosetresin, a natural rubber, or a synthetic rubber.
 4. The method of usingthe surface material of the molding surface of claim 1 wherein the moldis a mold employed for molding a resin in which the molding surface onwhich the titanium oxide coating film is formed reaches from 100° C. to400° C. during the using through contact with molten resin or throughheating the mold.
 5. The method of using the surface material of themolding surface of claim 2 wherein the mold is a mold employed formolding a food product, a thermoplastic resin, a thermoset resin, anatural rubber, or a synthetic rubber.
 6. The method of using thesurface material of the molding surface of claim 2 wherein the moldingsurface on which the titanium oxide coating film is formed reaches from100° C. to 400° C. during the using through contact with molten resin orthrough heating the mold.